The offset lithographic printing process utilizes a developed planographic printing plate having oleophilic image areas and hydrophilic non-image areas. The plate is commonly dampened before or during inking with an oil-based ink composition. The damping process utilizes an aqueous fountain solution such as those described in U.S. Pat. Nos. 3,877,372, 4,278,467 and 4,854,969. When water is applied to the plate, the water will form a film on the hydrophilic areas (i.e. the non-image areas of the plate) but will contract into tiny droplets on the oleophilic plate areas (i.e. the image areas). When a roller carrying an oil-based ink composition is passed over the dampened plate, it will be unable to ink the areas covered by the aqueous film (the non-image areas), but will emulsify the water droplets on the water repellant areas (the image areas) which will then take up ink. The resulting ink image is transferred ("offset") onto a rubber blanket, which is then used to print a substrate such as paper.
Conventional lithographic plates can easily be damaged by "fingerprint" that occurs during the pressman's handling of the plate during set-up. More particularly, oils such as squalene and other oleophilic substances are transferred from the pressman's hands to the printing plate surface, thereby affecting the carefully delineated hydrophilic and hydrophobic areas of the plate. This causes the first several images printed by the plate to be defective. The printable media of the present invention do not suffer from this "fingerprint" problem.
Lithographic printing plates can be manufactured using a mask approach and a dye-based hot melt ink jet ink. For example, U.S. Pat. No. 4,833,486 discloses a dye-based hot melt ink composition which is jetted onto a conventional photopolymer plate. The deposited ink acts as a mask during plate exposure, and is removed from the plate together with the exposed photopolymer during development of the plate. This technique involves multiple processing steps such as UV-irradiation, chemical development and plate drying, which result in high production costs and environmental concerns.
It has been proposed to apply "direct" ink jet printing techniques to lithographic printing. For example, European Patent Publication No. 503,621 discloses a direct lithographic plate making method which includes jetting a photocuring ink onto the plate substrate, and exposing the plate to UV radiation to harden the image area. An oil-based ink may then be adhered to the image area for printing onto a printing medium. However, there is no disclosure of the resolution of ink drops jetted onto the substrate, or the durability of the lithographic printing plate with respect to printing runlength.
Canadian Patent No. 2,107,980 discloses an aqueous ink composition which includes a first polymer containing a cyclic anhydride or derivative thereof and a second polymer that contains hydroxyl sites. The two polymers are thermally crosslinked in a baking step after imaging of a substrate. The resulting matrix is said to be resistant to an acidic fountain solution of an offset printing process. The Examples illustrate production of imaged plates said to be capable of lithographic runlengths of from 35,000 to 65,000 copies, while a non-crosslinked imaged plate exhibited a runlength of only 4,000 copies.
Both of these direct lithographic proposals require a curing step, and the Canadian patent illustrates the importance of this curing step to extended runlengths. The present invention eliminates the need for such a thermal or irradiation steps while providing a direct lithographic plate capable of a runlength of at least 100,000 copies.
It is known to improve the resolution of ink jet printers by applying an ink receiving layer to substrates such as metal, plastic, rubber, fabrics, leather, glass and ceramics, prior to printing thereon. See, for example, European Patent Publication No. 738,608 which discloses a thermally curable ink receiving layer containing a first water soluble high molecular weight compound having a cationic site in the main polymer chain and a second water soluble high molecular compound having a side chain containing a condensable functional site. Alternatively, the second high molecular weight compound may be replaced with a monomer or oligomer having at least two (meth)acryloyl sites, which results in a UV radiation curable ink receiving layer. In either case, the cationic site of the first polymer is said to permit an ink solvent to readily penetrate the ink receiving layer. The ink receiving layer of the present invention does not require either a thermal or irradiation curing step.
Porous ink receptive layers are also known. European Patent Publication No. 738 608, discussed above, suggests the inclusion of pore-bearing fine particles of an organic or inorganic material in order to attain quick absorption capacity in terms of absorption speed and absorption volume for an ink-receiving layer. Pigments such as silica and clay are suggested as the inorganic particles. Other references which disclose clay-containing substrates, as opposed to clay-containing layers supported on a substrate, include U.S. Pat. Nos. 4,833,486 and 5,364,702.
U.S. Pat. No. 4,833,486 discloses an ink jet image transfer lithographic apparatus which jets melted hydrophobic ink onto aluminum or paper plates, with paper plates having a high clay content found to be useful and economical. No discussion of specific clays or porosity of the plate is provided.
U.S. Pat. No. 5,364,702 discloses an ink-jet recording layer supported on a substrate, with the ink receiving layer containing at least one of acetylene glycol, ethylene oxide addition product and acetylene glycol and acetylene alcohol, each of which have a triple bond in its molecule. The ink receiving layer may also contain an inorganic pigment such as silica, a water-soluble polymeric binder, and a cationic oligomer or polymer. No discussion of porosity is provided. The printable media of the present invention employs a copolymer having a plurality of amine sites, which are at least partially neutralized with an acid.
U.S. Pat. No. 5,820,932 discloses a process for the production of lithographic printing plates. Ink jet liquid droplets form an image upon the surface of a printing plate corresponding to digital information depicting the image as provided by a computer system which is in communication with the printer heads. The droplets from the printer head comprise resin forming reactants which polymerize on the plate surface, alone or in combination with reactant precoated on the plate, to form a printable hard resin image. The resin image so formed provides a lithographic printing plate useful for extended print runs. In contrast, the present invention does not require polymerization of the fluid composition jetted upon the printable media substrate.